exim4-base 4.90.1-1ubuntu1.2 (amd64 binary) in ubuntu bionic

 Exim (v4) is a mail transport agent. exim4-base provides the support
 files needed by all exim4 daemon packages. You need an additional package
 containing the main executable. The available packages are:
 .
  exim4-daemon-light
  exim4-daemon-heavy
 .
 If you build exim4 from the source package locally, you can also
 build an exim4-daemon-custom package tailored to your own feature set.
 .
 The Debian exim4 packages have their own web page,
 http://wiki.debian.org/PkgExim4. There is also a Debian-specific
 FAQ list. Information about the way the Debian packages are
 configured can be found in
 /usr/share/doc/exim4-base/README.Debian.gz, which additionally contains
 information about the way the Debian binary packages are built. The
 very extensive upstream documentation is shipped in
 /usr/share/doc/exim4-base/spec.txt.gz. To repeat the debconf-driven
 configuration process in a standard setup, invoke dpkg-reconfigure
 exim4-config. There is a Debian-centered mailing list,
 pkg-exim4-users@lists.alioth.debian.org. Please ask Debian-specific
 questions there, and only write to the upstream exim-users mailing
 list if you are sure that your question is not Debian-specific. You
 can find the subscription web page on
 http://lists.alioth.debian.org/mailman/listinfo/pkg-exim4-users